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This is an article about the star, for other uses please see Mizar (disambiguation)
Mizar and Alcor in constellation Ursa Major
Mizar
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 13h 23m 55.5s
Declination +54° 55′ 31″
Apparent magnitude (V) 2.23
Characteristics
Spectral type A2 V/A2 V/A1 V
U-B color index 0.09
B-V color index 0.13
Variable type ?
Astrometry
Radial velocity (Rv) −9 km/s
Proper motion (μ) RA: 121.23 mas/yr
Dec.: −22.01 mas/yr
Parallax (π) 41.73 ± 0.61 mas
Distance 78 ± 1 ly
(24 ± 0.4 pc)
Absolute magnitude (MV) 0.33
Other designations
Mizat, Mirza, Mitsar, Vasistha, 79 Ursae Majoris, HR 5054, BD +55 1598A, HD 116656, GCTP 3062.00, SAO 28737, FK5 497, GC 18133, ADS 8891, CCDM J13240+5456, HIP 65378.

The Mizar-Alcor stellar sextuple system consists of the quadruplet system Mizar and the binary system Alcor.

Mizar (ζ UMa / ζ Ursae Majoris) is a quadruplet system of two binary stars in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23 and its spectral class is A1V. Mizar's name comes from the Arabic مئزر mīzar, meaning a waistband or girdle.)

With normal eyesight one can make out a faint companion just to the east, named Alcor or 80 Ursae Majoris. Alcor is of magnitude 3.99 and spectral class A5 V. Mizar and Alcor together are sometimes called the "Horse and Rider," and the ability to resolve the two stars with the naked eye is often quoted as a test of eyesight, although even people with quite poor eyesight can see the two stars. Arabic literature says that only those with the sharpest eyesight can see the companion of Mizar. Astronomer Sir Patrick Moore has suggested that this in fact refers to another star which lies visually between Mizar and Alcor. Mizar and Alcor lie three light-years apart, and though their proper motions show they move together (they are both members of the Ursa Major Moving Group), it was long believed they do not form a true binary star system, but simply a double star. However, in 2009, it was reported by astronomer Eric Mamajek and collaborators that Alcor actually is itself a binary, consisting of Alcor A and Alcor B, and that this binary system is most likely gravitationally bound to Mizar, bringing the full count of stars in this complex system to six. [1] Their study also demonstrated that the Alcor binary and Mizar quadruple are much closer together than previously thought - approximately 74,000 +- 39,000 Astronomical Units [2].

In Japanese mythology, Alcor is known as the lifespan star or "jumyouboshi" (寿命星)as it was believed that one who could not see this star would pass away by year's end. Of incidental note, the popular Japanese manga, Fist of the North Star, used this legend as a model for its death omen star (死兆星), in which it was said that people who saw the star would die later in the year.

More components of the Mizar system were discovered with the advent of the telescope and spectroscopy; a fine, easily-split visual target, Mizar was the first telescopic binary discovered—most probably by Benedetto Castelli who in 1617 asked Galileo Galilei to observe it. Galileo then produced a detailed record of the double star. Later, around 1650, Riccioli wrote of Mizar appearing as a double. The secondary star, Mizar B, has magnitude 4.0 and spectral class A7, and comes within 380 AU of the primary; Mizar A and Mizar B take thousands of years to revolve around each other.

Mizar A was the first spectroscopic binary to be discovered, by Pickering in 1889. Some spectroscopic binaries cannot be visually resolved and are discovered by studying the spectral lines of the suspect system over a long period of time. The two components of Mizar A are both about 35 times as bright as the sun, and revolve around each other in about 20 days 12 hours and 55 minutes. Mizar B was later found to be a spectroscopic binary as well, its components completing an orbital period every six months. In 1996, 107 years after their discovery, the components of the Mizar A binary system were imaged in extremely high resolution using the Navy Prototype Optical Interferometer.

Alcor
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension 13h 25m 13.5s
Declination +54° 59' 17"
Apparent magnitude (V) +3.99
Absolute magnitude (V) +2.01
Distance 81.2 ± 1.2 ly
(24.9 ± 0.4 pc)
Spectral type A5V
Other designations
Saidak, Suha, Arundhati, g Ursae Majoris, 80 Ursae Majoris, HR 5062, HD 116842, BD +55 1603, HIP 65477, SAO 28751, GC 18155, ADS 8891, CCDM J13240+5456

The whole four-star system lies about 78 light-years away from Earth. The components are all members of the Ursa Major moving group, a mostly dispersed group of stars sharing a common birth, as determined by proper motion. The other stars of the Big Dipper, except Dubhe and Alkaid, belong to this group as well.

Other Names

Mizar is known as Vasistha and Alcor is known as Arundhati in Indian astrological books. Mizar is Chickadee and Alcor is his cooking pot in the Mi'kmaq myth of the great bear and the seven hunters.

See also

External links

Coordinates: Sky map 13h 23m 55.5s, +54° 55′ 31″








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